1. Field of the Invention
The present invention relates to a method for manufacturing a gate for semiconductor devices, and more particularly a method for manufacturing a gate for semiconductor devices in which a TaON thin film is used as a gate dielectric film.
2. Description of the Related Art
Generally, in highly integrated semiconductor devices, the thickness of the gate oxide film in the semiconductor devices having a line width up to 0.1 xcexcm has to be decreased below 40 xc3x85 in order to achieve an reduction in short channel effect and an efficient control of channels. However, such gate oxide films tend to suffer from increase leakage current resulting from direct tunneling effects. As a result, characteristics of the transistor and the capacitor will tend to be degraded. Accordingly, in order to solve this problem, a Ta2O5 film has been proposed as a substitute for SiO2. The Ta2O5 film is a metallic oxide film having a high dielectric constant that can be used as a gate dielectric film in a transistor.
FIG. 1 is a cross-sectional view illustrating a conventional method for manufacturing a gate in a semiconductor device. As shown in FIG. 1, according to the conventional gate manufacturing method, a Ta2O5 film 2 is deposited as a gate dielectric film on a semiconductor substrate 1. The Ta2O5 film, which is a metallic oxide film having a high dielectric constant, is formed using tantalum ethylate (Ta(OC2H5)5) as a raw material and O2 or N2O as a reaction gas. A polysilicon film 3 is formed as a gate electrode over the Ta2O5 film 2. Subsequently, although not shown, a gate is formed according to a known method and the process of manufacturing the transistor is subsequently continued to complete the device.
However, the Ta2O5 film has an unstable chemical composition due to an unbalanced stoichiometric ratio. Therefore, substitutional Ta atoms may exist in the thin film due to the difference in the compositional ratios of Ta and O.
Also, since there may be impurities, for example, carbon atoms or carbon compounds and H2O resulting from the reaction of tantalum ethylate (Ta(OC2H5)5) and O2 or N2O gas, the transistor gate may exhibit an increased leakage current. Thus, the dielectric characteristics of the device may be degraded.
In order to suppress the excess leakage current and to prevent the resulting degradation of the dielectric characteristics, it is necessary to conduct an additional oxidation process to oxidize the substitutional Ta atoms remaining in the Ta2O5 film so as to stabilize the inherently unbalanced stoichiometric ratio of the film. In addition, after the deposition of the Ta2O5 film, it is typically necessary to conduct multiple low-temperature or high-temperature treatments.
Therefore, an object of the present invention is to solve the above-mentioned problems in the related art. Thus, an object of the present invention is to provide a method for manufacturing a gate for semiconductor devices, which is capable of suppressing the generation of leakage current of a gate by using a TaON film having a stable stoichiometric ratio as the gate dielectric film.
In accordance with one aspect of the present invention, a method for manufacturing a gate for semiconductor devices comprises the steps of: forming a nitride thin film on a semiconductor substrate; forming an amorphous TaON thin film over the nitride film; subjecting the amorphous TaON thin film to a thermal treatment at a high temperature to effect a crystallization thereof; and forming a polysilicon film as an upper electrode over the crystallized TaON thin film.
In accordance with another aspect of the present invention, a method for manufacturing a gate for semiconductor devices comprises the steps of: forming a nitride film on a semiconductor device; forming an amorphous TaON thin film over the nitride film; forming a nitride film or nitrified film over the amorphous TaON thin film; subjecting the amorphous TaON thin film to a rapid thermal process or a furnace thermal process to effect a crystallization thereof; and forming a polysilicon film as a gate electrode over the crystallized TaON thin film.